Tom Stoppard once said his favourite line in modern British drama was Christopher Hampton's in his second play, The Philanthropist (1970): "My problem is I'm a man of no convictions. At least, I think I am." That stylish dither has fuelled a remarkable career in theatre and films hardly equalled by Stoppard himself.

Slumped on a green sofa in his light-filled office overlooking Ladbroke Square in Notting Hill, Hampton stretches indolently and declares he has never been an "early morning" person. "I tend to scribble about in the morning - notes, look over what I did yesterday; the good hours for me are in the afternoon. Which is quite rare. A lot of writers I know, enviably knock off by lunchtime. Graham Greene used to finish at nine in the morning."

This seems a paradoxical image in one so notoriously hard-working. Hampton, who turned 60 at the end of January, has hardly drawn breath since his first play, When Did You Last See My Mother?, a rites of passage comedy of homosexual adolescence, was picked up by the Royal Court and produced in the West End in 1966, and the "marvellous boy" tag still fits a writer whose prodigious output - 12 films, 12 plays, countless adaptations, libretti and lyrics for Andrew Lloyd Webber (Sunset Boulevard) and Philip Glass (JM Coetzee's Waiting for the Barbarians), all executed with skill, wit and discretion - belies his cherubic, untroubled appearance.

Hampton is charming and gregarious, happy in his life - "I'm aware of how rare it is for people to be able to do exactly what they want to do, so I'm always grateful" - despite more than his fair share of setbacks (20 unproduced films) and critical vilification. This will be just an average sort of busy year. He has a new play in the West End this month, a new film going into production in late spring, a revival of his third play, Savages (1973), in July and a new Chekhov translation in November.

Savages, an indignantly eloquent examination of the Brazilian Indian "problem" under a tyrannous regime, and Chekhov's The Seagull, are part of the Royal Court's 50th anniversary year. Hampton's first four plays were produced at the Court, and when the then artistic director Max Stafford-Clark asked him for another in 1979 he declined, saying the theatre was for "new" writers.

The West End play is Embers, starring Jeremy Irons and Patrick Malahide, which Hampton has adapted from a novel by Hungarian Sandor Marai (who died in 1989). In its unfolding narrative of a friendship between two old men who both loved the same woman, it plies, in more melancholy and tragic vein, the same theme as Art, Hampton's 1996 runaway hit version of Yasmina Reza's Parisian comedy.

But it also demands a dramatic skill of compression that Hampton suggests is no easier than that required for his 1985 RSC version of Les Liaisons Dangereuses (he won an Oscar for the screenplay), where none of the characters actually meets in the original, and "where you have to invent the whole geography of it. With Embers one is doing a Racinian piece rather than ... well, something Tolstoyan. I've set it all in one place, deleted all the flashbacks and retained, I think, everything that is material."

The new film is Atonement, adapted from Ian McEwan's award-winning chronicle of love and misinterpretations across generations. "McEwan has read every draft, and been rather assiduous. The revelation at the very end is the most complicated bit to work out in film terms. But I think we have."

There was a time when people used to ask Hampton if he was writing another play, or was it still "just" the adaptations. He doesn't make such distinctions, always trying to do something different so that he bores neither himself nor his audience. And he quotes with approval Flaubert's dictum that the most important thing is the absence of the author's personality. David Hare, Hampton's great friend and coeval at Lancing College in the 1960s, regretted that Hampton's talent was hidden in serving someone he considered to be a lesser writer, Reza, when he adapted Art.

"Yes, that was very Hare-ish of him, like being patted on the back with a mallet! A lot of people didn't like Art though not as many as those who liked it. It seemed to annoy some people in a way I didn't quite understand." What about Richard Gott's accusation that there was in the piece a rancid dislike of modern art bordering on the Nazi? Hampton explodes in laughter. "Idiotic. The painting was the McGuffin. It wasn't about art at all, but what you allow your friends and what you don't, and how carefully you have to step."

An even bigger chorus of disapproval greeted his film Imagining Argentina (2003), which he wrote and directed, using the opportunity presented by his Oscar to tackle the Galtieri regime. "I decided to do something which it would be difficult to finance at a time when, for once, I was bombarded with offers. It took me 14 years." It is a hard-to-watch movie, but important, and beautifully acted by Antonio Banderas as the persecuted theatre director who "imagines" what happened to "the disappeared", and Emma Thompson as his wife, who is savagely abducted and tortured, that you wonder if the film itself has become unjustly "disappeared".

"Although there are many distinguished Argentinian films, nothing has been done about this extraordinary moment in South American history when a gang of people decided they would kill everyone they disagreed with ... people who, by a strange quirk of fate, were brought down by Mrs Thatcher. I make no claims for it, but such a film was needed in the same way that The Killing Fields was needed. I was surprised it was so virulently received."

Without being an obviously "political" writer, Hampton can more justly be so described than many others. Broadly speaking, his work divides into pieces about art and artists - of which his third Court play, Total Eclipse (1968), anatomising the friendship of Verlaine and Rimbaud, was the first - and stories about relationships that throw light on political and historical situations. These categories overlapped most spectacularly, and successfully, in what remains his best stage play, Tales from Hollywood (1983), in which artistic endeavour in a hostile community - Von Horvath, Brecht and the Manns gathered round the pool - reveals a bitingly funny epic of the loss of idealism.

And unlike many of his theatrical contemporaries, Hampton actually lived through political upheaval. He grew up in Alexandria, where his father worked for Cable & Wireless. He had hoped to avoid boarding school in England, but the Suez crisis of 1956 put paid to that, and the family left on the last boat, an experience he recounted with elegant, Proustian poignancy in his autobiographical White Chameleon (1991) at the National; a film may yet transpire.

Although only 10, he knew the Suez adventure was "horrendously" misguided. "My father certainly thought so. He was a solid Tory voter, but he had been posted there on and off since the 1930s and loved Egypt and the Egyptians." The bombing of his father's office by the RAF must have been the last straw. And Hampton was despatched on a new route to prep school, Lancing, and New College, Oxford, where he took a starred first in modern languages and sent his first play to the formidable agent, Margaret Ramsay, in London.

This led to the Royal Court and a fruitful collaboration with the director Robert Kidd. He had learned to enjoy himself at Oxford, he said, but the Court, where passions ran high, "gave me an education". The Lord Chamberlain disappeared during the run of Total Eclipse, which meant a couple of raunchy minutes could be replaced. Hampton never underestimated the cost of this victory over censorship: "For years people had been running at closed doors, using their heads as battering rams; now the doors were open and all my generation had to do was saunter through them."

The film of that play did not emerge until 10 years ago, starring Leonardo DiCaprio as a youthful Rimbaud and David Thewlis as an uninhibited Verlaine. Again, it was rather dismissed by the critics, but Agnieszka Holland's sensitive and sensuous direction and various revivals of the stage play have suggested the work's durability as a testament to the shifting terrain of artistic innovation in a study of character, and, indeed, friendship.

Hampton became a film director by default 10 years ago when Mike Newell, who had just directed Four Weddings and a Funeral, declined an invitation to direct Hampton's Carrington (1995) screenplay, with the apology that he had just done one "little English film" and had no patience for another. The result was an exceptional account of the love affair between Dora Carrington (Thompson) and Lytton Strachey (Jonathan Pryce) that won two awards at Cannes, for Pryce as best actor and for Hampton (a special jury prize) in recognition of his directing debut.

On the rare occasions that he ventures into journalism, his remarks - on Kevin Brownlow's David Lean biography, Simon Callow's memoir about Margaret Ramsay - are generous, informed and definitive. Does he envy Hare's eagerness to take up cudgels, assume the role of Osborne? "Not at all. I'm delighted someone's doing it and doing it so well. I admire his work but it is completely different from mine. I tend not to do journalism because I don't have that kind of facility."

Instead, he shuttles between his office and a Kensington mansion where he lives with his wife, Laura, with whom he has two daughters, Alice, a Montessori teacher working in the Cayman Islands, and Mary, starting out as a folk singer. "I don't take many holidays, but I do like travelling and hot weather. I don't take a great pile of books, perhaps two or three." He once took Donna Tartt's A Secret History, another one he wanted to turn into a film. It remains unmade, he says, with a philosophical shrug and a rueful smile.